Marking and switching system



Feb. 2, 1954 s. T. BREWER 2,668,195

MARKING AND swITcHING SYSTEM Filed Dec. 29, 1949 9 sheets-sheet 1 TTORNE Y Feb 2, 1954 s. T. BREWER MARKING AND SWITCHING SYSTEM Filed Dec. 29, 1949 9 Sheets-Sheet 2 nm. N OFN ATTORNEY Feb. 2, 1954 s. T. BREWER MARKING AND SWITCHING SYSTEM 9 Sheets-Sheet 3 Filed Dec. 29, 1949 /NVENTOR 5. 7. BREWER A TTOR/VEY Feb. 2, 1954 s. T. BREWER MARKING AND SWITCHING SYSTEM 9 Sheets-Sheet 4 Filed Dec. 29, 1949 INVENTOR By SJ.' BREWER QSSQM. Ng .SSN

ATTORNEY Feb. 2, 1954 s. T. BREWER MARKING AND SWITCHING SYSTEM 9 Sheets-Sheet 5 Filed Dec. 29, 1949 /NVENTOH By 5. 7. BREWER ATTORNEY Feb. 2, 1954 s. T. BREWER MARKING AND swITcHING SYSTEM 9 sheets-sheete Filed DSC. 29, 1949 /Nl/EA/TOR By sf BREWER n @Qu A7' TUR/VE Y Feb, 2, 1954 s. T. BREWER 2,668,195

MARKING AND swITCHING SYSTEM v Filed Dec. 29, 1949 9 Sheets-Sheet 7 LINE FRAME [V0.2 SIGNAL /N VENUR N By sr BREwgR QS @La @man L Feb. 2, 1954 5, T, BREWER 2,668,195

MARKING AND SWITCHING SYSTEM Filed Dec. 29, 1949 9 Sheets-Sheet 8 /NVE/vrof? S. 7.' BREWER ATTORNEY Feb- 2, 1954 s. T. BREWER 2,668,195

MARKING AND swITcHING SYSTEM Filed Dec. 29, 1949 9 Sheets-Sheet 9 FIG. 7 F/G. .9

FIG. .7

, /NVEA/of? By 5.7.' BREWER 9. 6. Sum- ATTORNEY Patented Feb. 2, 1954 seams MARKING AND SWITCHING SYSTEM Sherman T. Brewer, Chatham Township, Morris County, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 29, 1949, Serial No. 135,769

11 Claims.

This invention relates to telephone switching systems and more particularly to apparatus for testing and selecting a channel through the switching equipment.

An object of this invention is to provide improved switching circuits, methods and appa ratus for more rapidly and more economically establishing communication paths between subscribers stations.

A feature of this invention is the provision of a single group of junction means which is selec-- tively associable with the several groups of switches.

Another feature of this invention is the separating of channel selection and supervisory functions whereby the means for performing the channel selection function may be used in comh mon by all of the switches.

A further feature of this invention is the prevision of greatly simplified junction means.

Another feature of this invention is the provision of junction means provided with a mutual lock-out feature and provided with automatic releasing means.

Other objects and features of the invention will become apparent in the ensuing general and` detailed descriptions of a preferred embodiment of the invention.

In the exemplary embodiment set forth herein, the cross-point relays are so-called reed relays 'comprising one or more sets of contacts sealed in individual glass containers or other suitable 'envelopes with a relay winding circumferential to the envelopes.

When desired, a polarizing magnet may also be associated with each of the relays or in some cases with each of the contacts Vequipment are arranged so that a subscriber in initiating a call rst sets his calling device in ac,- cordance with the number or symbols designating the called subscribers station. The subscriber may then check the accuracy of the setting of his equipment and if it is found to be properly conditioned the subscriber will then place his call by picking up the receiver or hand- `set in the usual manner. As a result, the subseribers calling equipment is connected and maintained connected to the line extending between the subscribers station and the central station. The subscriber in initiating a call will then set into operation the equipment at the central station for applying a low frequency alternating current to the calling subscribers line and for 'extending the transmission path from this line to certain call receiving and recording equipment. When these connections are established pulses are transmitted through the subscribers calling device which will be received, recorded and checked by equipment at the central station. Thereafter a path is established from the register or receiving equipment through a number group circuit to determine the location of a called line or outgoing trunk circuit. The control equipment then transmits a signal to a circuit individual to the subscribers line and also applies a marking voltage to a terminal associated with a trunk group. The circuit individual to the subscribers line then applies a marking voltage and an identifying signal to the switching network.

In the exemplary embodiment set forth herein the switching network comprises a plurality of stages each stage of which comprises a group of relays arranged in a coordinate array. Each relay has associated with its winding a twoelement gas-filled cold cathode tube. In the preferred embodiment of the invention each of the relays comprises a plurality of reed contacts each enclosed in a glass envelope and surrounded by an operating winding. Speciiically, a group of such relays comprises in effect a switch. The switches are arranged on frames and in accordance with the exemplary embodiment herein one group of switches is called a line frame and another group of switches is called a trunk frame. A plurality of line frames and a plurality of trunk frames with their appropriate interconnections comprise the switching network. Each of these frames is provided with two groups of switches of the type described above. These groups of switches are usually called the primary group of switches and the secondary group of switches, and the primary and secondary switches are inter-connected in a manner similar to that employed in cross-bar switching systems. Interposed the two groups of frames are junction means or mactors each comprising a negative resistance element such as a cold cathode multielement gaseous conduction tube. These mactor tubes are arranged in a lock-out circuit and are self-extinguishing.

In the originating phase of a call, a marking condition is applied to only one of the subscribers line terminals and to one or more terminals associated with idle trunks at the end o the switching equipment. This marking voltage which is applied to the line terminal causes the two-element gas tubes associated with various idle cross-points leading from the marking terminal to have a discharge initiated through.

them. Thus, discharges are initiated through all' of the tubes associated with idle cross-points of the primary line switch associated with the marked line. The discharge current iiowing through these tubes in turn relays the marking condition to other two-element gas discharge tubes associated with the idle cross-points of the secondary line switches through which possible paths extend from those primary cross-points having discharged tubes. Thus, the discharge through these tubes marks and relays a voltage condition through all of the idle paths from the marked line terminal to the group of mactor circuits associated with the line frame.

In addition to applying the marking voltage, the circuit individual to the subscribers line transmits a signal indicative of the one of the several provided line frames with which the subscribers station is associated. This signal operates selective means associated with the junction means or mactor circuits whereby but one line frame may utilize the provided mactors at any one time. Therefore, only one group of mactors need be provided for all provided line frames.

The marking condition applied to the trunk terminal is relayed through the trunk frames in a manner similar to the manner described above with reference to the line switch frame. If the trunk group comprises more than one trunk the trunks of this trunk group will be associated with dierent trunk frames. When it is desired to select a trunk of this group one idle trunk on each trunk frame of this group is marked. A marking voltage is relayed from all of the marked trunks through their respective primary and secondary switches. Certain of these marking voltages from the trunk frames are then applied to the junction means or mactors intermediate the line and trunk frames in accordance with which of the above-mentioned selective means has been operated by the signal transmitted from the subscribers line circuit. Those trunk frame secondary switch outlets which are associated with secondary switches in the utilized line frame are connetced to the provided mactors so that the trunk frame marking voltages may be applied to the mactors, but those trunk frame secondary switch outlets associated with other line frames are not given access to the mactors. These marking voltages from the line frame and trunk frames are applied to dinerent elements of tubes in the idle mactor circuits and are or suilcient magnitude to initiate a discharge through one or more of these tubes. However, as pointed out herein, these tubes have their elements connected to provide lock-out between the various tubes so that the discharge transfers to the main discharge path in one of the tubes only. This discharge then determines which oi the idle paths from the marked line terminal to one of the marked trunk terminals will be utilized.

It should be noted that the negative resistance element or mactor tube operating in a lock-out circuit as described above not only selects an idle path through the switching system but also selects an idle trunk in a group of marked idle trunks. Thus both an idle path through the switching system and an idle trunk are selected with one operation, namely the initiation and transfer of the discharge across the main gap of one of the cold cathod gas discharge tubes of one mactor only.

While the above description assumes cold cathode two-element or multielernent gas dischargel tubes, it is to be understood that hot cathode gas discharge tubes as well as vacuum tubesl may be employed if so desired.

Thel cold cathode gas discharge tubes referred to herein have two or more electrodes enclosed within a gas-tight envelope containing gas at a reduced pressure. The gas will usually comprise argon, neon or mixtures of these gases but may also comprise other inert gases as well as other gases and vapors such as mercury vapor, etc.

Upon the initiation of a discharge within a selected mactor tube and transfer across the main discharge path of that tube a circuit is completed for the operation of a relay, which relay in operating increases the current ilcw through the gas discharge tubes of the Selected path and causes the relays at the associated cross-points to operate and to close their contacts thus establishing a metallic path through the switching system.

The tubes in the mactors are arranged to be self-extinguishing, and after a suitable interval the discharged tube is extinguished and the mactor relay released. This results in the iinal extinction o all of the gas discharge tubes in the selected path.

Supervision of the connection is continuous between the selected trunk and the subscribers line circuit as is permitted by the use of a unidirectional current conducting device or varistor in the sleeve lead of the selected path. By this means, the necessity of relaying supervision through the junction means or mactor is avoided whereby the provided mactors may be used in common by all line frames as above mentioned.

Upon the establishment of a path to an idle trunk, the circuit connections within the office change so that alternating-current power for the operation of the calling device at the subscribers station is supplied from the selected trunk circuit through the closed contacts of the switching system. This alternating-current power causes further pulses to be generated by the subscribers equipment designating the called subscribers station, which pulses are then transmitted from the subscribers line, through the selected switching path through the switching system', and then over a trunk circuit either to the subject office or to a second central oiice depending upon the oiiice designated. At the second central cnice, certain of the pulses are employed to establish a connection through that ofce in a manner similar to that described above and when sufricient information has been received at the iinal central oiiice to establish a connection tc the called subscribers line a signal is sent back to the first ofce which is repeated through the subscribers station which causes the equipment there to be switched from the calling or dialing condition to a telephone transmission condition. At the termination of the call the circuits are returned to normal by removing the calling potential to the various terminals of the switching equipment which allows the relays to release and to be restored to their normal or idle condition.

paratus to said talking apparatus.

l Novel features of the subject circuits disclosed but not claimed herein and full disclosures of elements schematically represented herein are presented and claimed in United States Patent 2,655,559 granted October 13, 1953, to W. A. Malthaner-H. E. Vaughan, and in the United States patent application of S. T. Brewer- E. Bruce, Serial No. 115,962, filed September 16, 1949, and in patents and applications cited therein, all of which are incorporated herein by reference.

The operation of the present embodiment of the invention may be more fully understood by the following brief description with reference to the simplified block schematic of Fig. 1 which shows in outline form various circuits and the manner in which they cooperate in a central oflice of the type embodied in the invention.

As shown in the drawing each office is provided with a switching network usually located on a plurality of supporting frames. Two line frames and two trunk frames are shown in the drawing and are arranged to handle calls within the ofiice and between oiiices to and from subscribers lines in each oiii'ce by trunk circuits, of which four incoming and three outgoing trunks and a busy-tone trunk are shown in the drawing. Four subscribers lines are shown connected to the depicted office. While only a few subscribers stations, lines, trunks, frames and other circuits and apparatus are shown in the drawing, it is to be understood that any suitable number of the different circuits and ap'- paratus may be provided. Only a limited number are shown in the drawing and described herein because the additional circuits will be substantially the same as those shown and will operate and cooperate with each other and the other circuits and equipment in a manner similar to the operation and cooperation of the circuits shown and described herein. i Each subscribers station comprises apparatus for producing an audible ringing signal at the station in response to power transmitted from the central oce, switchhook apparatus for in'- dicating to the central oiiice that the telephone s et is on or oif of its cradle, apparatus for generating dialing signals in response to power transmitted from the central oiiice, talking apparatus and apparatus for switching under control of the central ofiice from said signaling ap- A suitable form of subscribers station equipment which will cooperate satisfactorily with the exemplary embodimentset forth herein is more fully disclosed in United States Patent 2,598,695 granted June 3, 1952, to H. E. Hill-D. B. Parkinson, and the disclosure thereof is hereby incorporated in this application by reference. Y

Common control apparatus is provided at each central oice for establishing talking paths through the switching network on a one-at-atime basis, either in response to dialing signals received from a subscribers station associated with the same central office, or in response to dialing signals transmitted from a subscribers station associated with another central office, through the other central oflice and over a trunk circuit from said other central office.

. `The number of switches per switching frame and the number of such switching frames provided can be expanded in an obvious manner together with suitably provided common control circuits of v.the type represented to furnish satisfactory s'ervi-4 The 'amount of equipment to be installed will vary with the number of -subscribers, the calling habits of the subscribers, and the operating times of the apparatus. The particular types of apparatus intended for the physical embodiment of the invention have sufliciently fast operating characteristics that satisfactory service can be provided on a one-at-atime basis to a group of subscribers of the size now commonly associated together in onev central oflice.

The central oflice of Fig. 1 comprises subscribers stations, such as station H0, equipped with preset repetitive dialing means; line conductors, such as conductors extending between the subscribers station and individual central oice line circuits, such as line circuit H2; outgoing trunk circuits, such as trunk H3; and incoming trunk circuits, such as trunk circuit i I4; together with a switching network comprising line frames, such as the No. 1 line frame H9; and trunk frames, such as the No. 1 trunk frame |29; by means of which desired connections may be established between any of said subscribers stations and any of said outgoing trunks, or between any of said incoming trunks and any of said subscribers stations.

Associated with the olce are common control circuits, shown in Fig. 1 below the switching network, comprising an originating actuator |2| for transmission of power to a subscribers station for causing thereat the generation of dialing signals designating a called destination; originating receiver and register circuits |22 for receiving such dialing signals from a calling subscribers station and registering the information as to the desired destination; a connector circuit |23; and a trunk number group circuit |24 for identifying the location of the desired outf going trunks on the switching network, performing an idle-busy-vacant test on such designated trunks and for establishing, in part, a connection ythrough the switching network from the calling subscriber to one of said designated outgoing trunks. The common control equip.- ment also includes an outward actuator |30 for supplying signal generating power to a calling subscribers station from an outgoing trunk circuit and back through the switching network after a connection between the subscribers station and a designated outgoing trunk has been established so that dialing or 'calling signals representing the desired called destination may again be generated at the subscribers station and transmitted through the switching network and through the outgoing trunk 4for use in establishing subsequent connections `toward the called destination.

For the establishment of a terminating connection between an incoming trunk and a 'called subscribers station, the common control equipment also includes an incoming receiverV and register |35 for receiving the dialing signals des'- ignating said called subscribers station after transmission from a calling subscribers subset through one or more switching systems, through an outgoing trunk circuit, and over an interconnecting trunk to an incoming trunk circuit of this terminating oiiice; a connector circuit |36; and a subscribers number group |31 for identifying the location of the said called subscribers station on the switching network and for making an idle-busy-vacant test of said called station and for controlling the establishment'in part, at least, of a connection between said incoming trunk circuit and said called subscribers station through the switching network.

Outgoing connections from an outgoing trunk of. this cnice may terminate either in an incoming trunk of this same cnice for establishing a connection to a called. subscriber in the same cnice, for example the connection I MI, shown be- *weon outgoing trunk I i3 and the incoming trunk IH both in the office of Fig. 1, or such connection from an outgoing trunk may terminate in an incoming trunk in another oice for the establishment of a connection to a designated called station in said other office, for example the connection |42 extending from the outgoing trunk |43.

Amore detailed description with reference to thesev figures will now be made of the establishment of a connection between a subscriber in the oice shown in` Fig. 1 and a designated called subscriber in either the same or a diierent oice. Assume, for example, that the subscriber provided with subset I I desires to make such a call. He first presets the signal generating apparatus in. his subset in accordance with the numbers or symbols representing the designation of the called subscribers station to which he desires to establish connection. With the complete desired number preset, the subscriber then removes the telephone set from its cradle or switchhook thereby completing a direct-current circuit over conductors III for the operation of a line relay in line circuit l I2, associated with his station. The operation of said line relay causes the operation of another relay in line circuit H2 for connecting an originating actuator I2I and receiver |22 to the line I l I and for removing said original direct-current line relay from the conductors I l I connecting said calling subset to the central oiiice. The operation or said relay for connecting said calling line to the originating actuator I2I and receiver I22 is made in conjunction with a cold cathode gas tube associated with the line circuit, which gas ltube is connected in lock-out with other similar gas tubes in other line circuits as is indicated by lock-out element 144. Therefore', in the event that two or more subscribers simultaneously remove their' telephone sets from the cradles or s'witchhooks, only one of such subscribers will be immediately connected to said originating actuator, and all other said calling stations will be temporarily held with only their direct-current line relays operated awaiting ac cess toA an originating actuator and receiver until the 'rst selected subscriber has been served. The types of gas tube lock-out circuits employed in the present embodiment of the invention and the opera-tion of these lock-outs are set forth more fully in United States Patent 2,350,888, granted to N. I. Hall on June 6, 1944, and .the disclosure-of said patent is hereby incorporated in this specification by reference.

Upon the connection of the subscribers subset LVI 0 via line circuit I l2 to the originating actuator I-2I.,. i5-cycle alternating-current power is transmittedirom said actuator to said calling subscribers subset to cause signal generating apparatus in that subset to generate calling or dialing signals representing the called subscribers station designation as preset' on the calling subscribers subset. A complete' called designation might consist, forV example', of three symbols or numbers designating thev called subscribers central oiiice, four digits designating theY called subscribers line number in vsaidoice and an additional 'sym-bol designating the party letter of 'the called subscriber associated with saidfcalledf line.

Under the' control of the actuatorv these eight symbols or numbers designating the complete called number are rapidly generated repetitively.

During the intervals in which an actuator is supplying alternating-current power to a called subscribers subset, the connection betweenthe calling line circuit and the central cnice switching and control equipment is held under control of a monitoring detector inthe alternating-current power path so that, if the calling subscriber returns his telephone set to its cradle or switchhook during such interval, the interruption of this now of power currentlthrough the subset will result in the release of the connections thus far established for the call and the return to normal of all of the associated circuits.

Associated with originating actuator I2I is the originating receivei` and register circuit |22. Said originating receiver examines the dialing signals generated in the calling subscribers Subset and transmitted to the receiver through the line circuit and through the originating actuator. The originating receiver and register |22 then proceeds to decode and register the numbers or symbols represented by the subsequent dialing signals. Suitable receiver and register circuits employed at this point in the present embodiment of the invention may be of the type disclosed in United States Patent 2,615,971 granted October 28. 1952, to Malthaner-Newby-Vaughan. and in United Patent 2,658,188 granted November 3, 1953, to Malthaner-NeWby-Vaug'han, and the disclosures' of said applications are hereby made a part of the present disclosure as ifY Set'v forth fully herein.

In the present embodiment of the invention, said originating receiverv is arranged to decode and register only those symbols or numbers which designate the called central office, and as in the example mentioned above, such central cnice is commonly designated by three symbols or digits which ordinarily will be arranged to occur at the beginning of each complete number transmitted from a subset. When receiver and register |22 has registered the symbols or numbersy designating the called central office, it connects itself through a connector circuit I23, connected in lock-out with other similar connectors as indicated by lock-out element'A M5, to the trunk number groupAIZll^ for locating an idle trunk to said designated oice. Lock-out is required between connector i23- and other similar connectors because of the one-at-atime operation or the switching network. The method of testing for idle paths through the switching network in the selection of such an idle path for use ina corinection, as set forth hereinafter for the present embodiment of the invention, requires that such testing and selectionoi paths through the switching network be performed on` a one-at-tirne Iu-rtlfier,A the testing and selection of paths through the switching network may be performed either by receiver I2-2 witlfiv number group i26- or by receiver I`35` with number group I'3l, or in a large cnice a plurality of receivers similar to 122 may be provided, each withv access to number group I24 and a plurality oi receivers similar to |35 may be provided each withl access to'number group 131, witheach receiver serving either a group of line circuits or'. a group or incoming trunk circuits. Thus, the lock-out arrangement between' number group connectors is required to .insure that' only lone connection between any number group circuit and a receiver exists at any one' time to` insurev tests and 'selections on the switching network` on a one-at-a-time basis.

Further, a large oice might be arranged with a plurality of originating actuators and receivers with each such actuator-receiver combination having access to an individual group of lines.

By means of cold cathodey gas tubes includedV in the trunk number group, an idle-busy-vacant test is made of the trunks in the designated trunk group and if there is one or more trunks idle in said designated trunk group, a relay in said receiver applies a voltage to a lead associated with said trunk group. One of the idle trunk circuits, of this trunk group, associated with each of the trunk frames is operated to extend this voltage to the sleeve lead appearances associated with idle trunks in said group at the trunk side f the switching network of the central oflice. If any of the outgoing trunks in the designated trunk group is in use in the path of a previously established connection, the voltage is not connected to such outgoing trunk leads but'is vcond nected only to the switching network appearances of the idle trunks in the group. Assume, for example, that the called oice designated by the numbers preset on calling subscribers subset H0, and registered in receiver |22 designates a subscriber in a distant oiiice.y By way of example, one circuit is shown in Fig. 1 for the establishment o f an interoiiice outgoing connection. This is shown by the circuit comprising outgoing trunk |43 which is connected Via interofce conductors |42 to an incoming trunk circuit in the distant oice. Thus, in this case, with outgoing trunk |43 idle a voltage is connected from the trunk number group |24 through this trunk to the appearance of its sleeve lead at the left vertical of primary switch |50 on the No. l trunk frame of the switching network of the shown oice. At the same time, a signal is transmitted from the originating conductor |23 to the calling line circuit I I2 for a purpose hereinafter to be noted.

The switching network comprises line frames and trunk frames. Both types of frames have primary and secondary switches or switching arrays of contacts. Each primary line and trunk switch or switching array has a number vof vertical input columns across the switch to which are connected line or trunk circuits respectively and a number of horizontal output rows across the switch. Each of these rows and columns consists of three conductors, two for the usual talking path and the third is the sleeve lead. At the intersection of each row and column, hereinafter called a cross-point, is a relay consisting of an operating coil and three sets of vmake contacts. Two of these contact sets when closed connect the talking conductors associated with the particular input column to the talking conductors associated with the particular output row. A cold cathode gas diode is also associated with each cross-point relay, and this diode in series with the winding of the relay is connected be- .tween the sleeve lead of the vertical input column and the sleeve lead of the horizontal output row. The third contact set of the cross-point relay, when operated, short-circuits its associated gas diode. The use of these cross-point gas diodes in the sleeve leads facilitates the identification and selection of idle paths through the switching network, as described hereinafter, and the short-circuiting of said diodes at operated cross-points facilitates the holding of an established connection through the network and the maintenance of a busy indication along said established connection during the path selection processes of subsequent calls.

Each secondary switch or switching array 'ls connected to form a similar rectangular array of cross-points except that the horizontal rows are used as input terminals and the vertical columns as switch outlets. However, in the secondary switches of the line frame, a fourth or control lead is also extended from each vertical, and the gas diode at the cross-point is connected between this control lead and the sleeve lead of the associated horizontal input row.

In addition, each line frame and each trunk frame comprises a number of such primary and secondary switches arranged so as to provide one talking path from each primary switch to each secondary switch. Specifically, for example, in Fig. 1 the line frame i |9, with which the calling subscribers station |||3 is associated, may comprise any suitable number of primary switches, two of which |5| and |52 are shown in Fig. 1 by way of example, each switch having a plurality of input columns, two of which are represented in Fig. 1. Each input column is connected to a line circuit individual to a subscribers station. Each line primary switch has a plurality, usually ten, of horizontal output rows, two of which, i. e., the first and last, are represented in Fig. 1. Line frame I9 also comprises a plurality of secondary switches, two of which, switches |53 and |54, are represented in the drawing. Each secondary switch is provided with horizontal inlets and a plurality of vertical outlets. The interconnecting conductors between primary and secondary switches, hereinafter called links, are connected as disclosed specically, for example, in line frame ||9 in which the upper primary switch |5| has its outlets connected to the upper inlet of the secondary switches, the top outlet of primary switch l5! connecting via path |55 to the top inlet of secondary switch |53 and the lower outlet of primary switch |5| connecting via path |56 to the top inletof secondary switch |54, and in which the lower primary switch |52 has its outlets similarly connected to the lower inlets of the secondary switches, the top outlet of primary switch |52 connecting to the lower inlet of secondary switch |53 and the lower outlet of primary switch |52 connecting to the lower inlet of secondary switch |53. Intermediate switches will usually have their intermediate and first and last levels connected in a similar manner. Two such line frames are shown in the office of Fig. 1 for disclosing the operation of those features of the system which relate to cooperation and differentiation between the frames.

The line frames can be readily expanded in an obvious manner so as to provide switches and frames of any desirable size, and -any desirable number of such frames may be provided having any desired number of input line circuits consistent with the operating times of the system and the calling habits of the subscribers and having a similarly consistent number of primarysecondary-link paths and secondary outlets. For

`example, line frames might be provided with Proceeding from the trunk output side of the switching network backwards through the oiiice,

a similar framearrangement is disclosed. Trunk frame. |25, for example, consists of a plurality 'of 'primary switches, such as switches |55 and |58, ,each having vertical multiples to each of Vwhich a trunk circuit is attached, such as trunks 114 and M3 connected to primary switch 150, and horizontal multiples each of which is connected to the horizontal input multiple of a secondary switch to provide onepath or link from each vprimary switch to each secondary switch, as shown by the indicated paths 153 and 50 between primary switch 150 and secondary switches 161 and 152.

The trunk frames can be readily expanded in an obvious manner so as to provide switches and frames of any desirable size, and any desirable number of such frames may be provided having a number of trunk connections consistent with the operating times of the system and the amount of traiiic to be handled and having a similarly consistent number of primary-secondary link paths and secondary outlets. For example, trunk frames might be provided comprising ten primary and ten secondary switches, each switch having i ten inlets and ten outlets. In such case the frame would provide connection between 100 trunk terminals and 100 secondary switch terminals.

Connections are made between the secondary line frame switches and the secondary trunk frame switches to provide ,talking paths between each line frame and each trunk frame. These connections comprise a direct metallic connection for the talking conductors of each path but the third or sleeve leads between the line frame secondary switches and the trunk frame secondary switches are each provided with a unidirectional current conducting .device or varistor, such as varistor 1'63.

VIntermediate the line frames and the trunk frames are a plurality of junction means, hereinafter termed mactors which select which of the idle paths through the switches is to be employed.

One oi these mactors is provided for each of the i links between the secondary switches in any one line frame and the associated trunk frame secondary switches. Thus, the control lead of the left vertical of line secondary switch 153 is associated with mactor M1, the control lead of the right vertical of switch i53 .is associated with mactor M2, the control lead of the left vertical of secondary switch 154 in the No. l line frame 119 is associated with mactor M3, and the control lead of the right vertical of secondary switch 154 is associated with mactor M4. Similarly, the control leads from the secondary switches of other provided line frames are associated with these same mactors, only one group oi` niactors being provided for all line frames. lSelective means are provided for enabling the mactors to be employed only by the line frame with which the utilized subscribers line circuit is associated as will be seen hereinafter.

In the particular exemplary call being described, it -has been determined that outgoing trunk 143 is available for service and that lit is .desired to connect the calling subscribers line 1.111 to this trunk. In response to the aforesaid signal from connector 23, Ythe line circuit H2 applies a line mark voltage to the switch sleeve lead associated with this calling .line at the right vertical inlet of primary switch i5! on the No. 1 line frame 19. This voltage fires gas diodes between this primary switch vertical line input and the .sleeve lead to each idle horizontal outlet ci said primary switch. Assuming, in this case, that line ,frame `119 is completely idle, gas diodes between the `aforementioned primary switch sleeve lead inlet and the sleeve lead outlet to each secondary switch nre, thereby altering the-voltage condition on the sleeve leads associated with pri mary-secondary link paths i555 and 15G. This altered link sleeve lead voltage, in turn, res the gas diodes in the secondary switches between said link sleeve leads and the control lead of each idle secondary line switch output path. Thus, in the case of a completely idle frame, gas tubes 'are fired in the primary and secondary switch sleeve lead along the idle path from the input terminal associated with line circuit 112, line link Ypath E55, to mactor M1, along similar individual idle paths from the said line circuit to mactors M2, M3 and M4 and also along other idle paths to other mactors not shown.

The line circuit i i2 also responds to the signal from connector 123 to transmit a line frame signal. 4Since line circuit 112 is associated with the No. l line frame 119, 'this transmitted frame signal is indicative of that fact. This signal is transmitted via conductor 165 and operates the No. 1 frame relay 166. It may be noted that had a line circuit associated with line frame No. 2 been employed, Athe signal would have been transmitted over conductor 161 to operate the No. 2

frame relay IBB.

With relay 68 operated, the sleeve leads vor those interframe links associated with the No. 1 line frame 113 are connected to the mactors. Thus, for example, the sleeve lead from the right vertical of trunk secondary vswitch 161 is associated with mactor Mi through a contact of operated relay E85, the sleeve lead of the right vertical of trunk secondary switch 162 is connected to mactor M3 thru a contact of relay 166, and so forth.

Therefore, with a frame relay such as relay IEB operated, the `voltage applied to the sleeve lead ofthe left `primary vertical of trunk iprimary switch i5@ Vassociated with the desired outgoing trunk 143 rires gasdiodes of the trunk frame primary and secondary switches and, in the case of a completely idle trunk frame, thereby establishes a connection through such nred diodes between said primary rvertical leads, trunk lilik path 159 to mactor M1, and other similariconnections are marked from the same said trunk vertical sleeve lead along similar individual paths to 'mactor M3 and also along other similar individual paths to other mactors not shown. If any of the link or mactor sections of any of the abovedescribed vpaths through the switching network is in use as part of a previously established connection, the voltage, established 'by virtue of Athe holding condition on the sleeve 'lead of Vsuch busy section, as hereinafter described, is such that the gas diodes will not iire between said 'busy sections andthe adjacent sections to which lvoltage marks have been extended.

Assuming only outgoing trunk 143 to be available, of Ythe various idle line 'frame and trunk frame paths now marked by ionized gas diodes and lshown on the drawing, only the Apaths vwith which maotors MI and M3 are associated form vpossible compiete paths between the calling line circuit i i2 and the desired trunk His. The other mactor circuits which have been marked from the line side, lfor example, mactor M2, terminate :at trunk frames other than trunk -frame 120 on which the `desired trunk appears. Each of the inactor circuits M1 and M3, by means of the combination of altered voltages on the two control leads connected to each said mactor recognizes that itis associated with apossible complete path through the switching network :and starts 'to Jfunction -to complete this path. A cold cathode 'i3 gas tube each of these maetors -is .connected in a lock-ou-tcircui-t as indicated .by lockecut ele@ ment 110, so that only one of 'said mactors Ywill succeed in fully operating. Assume for example, that in this case mactor Ml is taken into service and that :mactor AM3 is locked out. At this time a relay niactor Ml operates to reduce the im? pedance in the circuit through the gas diodes .and .cross-point lrelay coils associated with the ,sleeve lead path from the calling line to this mactor therebycausing sufficient .current to iiow .in said path to operate said cross-.point relays. A simi.- lar :reduction .of impedance .occurs in :the sleeve lead path from V:rnaotcr Ml Athrough the rp nary .and secondary `.Gross-point relays and diodes .of trunk `trame l2!! kto outgoing 'trunk .l 43 for .operalb-.lng the cross-point relays ,associated --witb path.. `The operation of thescuiour .cross-point relays .completes .a talking Connection between saidoallng.subscribers station HB .and outgoing trunk |43.

.Aitor a rsuitable interval :tl-,1e niaotor "tubo is self-eating looted path through the trunk frame, varistor 153, via the sleeve lead of the Vselected path .through the line vfratrie H9, and through the olf a supervisory relay in line circuit l l2.

lI n this manner, super-vision is obtained ,exten .nelly .o f the .mactor circuit.

The .common control equipment at the bottoni of Fig. l which was utilized in the originating phase of the .call is new released, and the trunk r .circuit proceeds with matters incident lto the ,terminating phase .of the. call. This pbaseoi .the call .iS .described in Tdetail in the above-cited .patent .granted to Maltha-ner-Vauehan and `the abovefoited application of Brewor-Bruceand ,applications ,and patents .cited therein, and the method of operation of .the nov-el fea-tures of the subject .invention is substantially identical on both `.phases yof va call, whether ,the Y,call be `interoihce of intraoce.

Detailed description e more completo understanding or the inveng. f.. and e line circuit in. iride-lai to each .of those ons;

'Ffig.. contains a representation :of .Certain .con-

ltrol equipment; i

litige`- .4 and 5 show the :primary and secondary Vswitches of a rst-and `a second line frame, re-

- spectively;

vthe drawings disclosed in detailn the above- .cited application .of Brewer-Bruce and in the lbltsfotsd patent granted to Malthaner... in applications vzand" patents Cil Cil

:thefigure of Athe drawing `on which the element.

appears. .the line relay ,Xin line .circuit 2&9 .(Fig. `2) will hereinafter :be :referred to .as "fnelay M2) Referring ii'rst to Fig. .2, a plurality of Sube scribers stations, such :as stations 20.492071 .are .provided with individual line circuits such as line circuits 26a-2%, respectively. The calling .subscriber, assumed 'to 'be the subscriber .at 4:station 204, presets the ldesignation .ofthe desired kcalled party and lifts his handset to close the switchE hook contacts olf his subset whereby a directeou-r.- rent circuit is 4established from ground at zithe No. 4 contact .of rela-y REQ) in line .circ-uitZDQ, which is individual .tostation 2M, Vconductor 22.8 No. .4 contact yof relay :60(2) .to the tip .conductor 209, through the closed switchhook contactdqring .conductor 2li), No. 3 contact of lrelay 00.629, .conductor 2H, No. 2 contact of relay 1RCY(-2') conductor 2fl2 and to battery -through the windv.ing lof line relay 11(2) whereby relay 15(2) operated.

:Prior to these operations, relay 21e is .operated over -a path from positive battery at the 'back contact of relay13t2 4in originating receiver 35H., conductor dat, resistor i214, winding of relay. i213 and to ground. Thereforawhen relay '11(2) op crates, positive battery, assumed v.to be positive IE5-:volt battery, applied through the front contact .of relay 213, resistor 21.5, .conductor 216, No. k3 .contacts .of relay L 2) and to the -rightehand main anode .ofv multielement gaseous .discharge vtube LA(2). 'Thisstube may 4`be .of the type dis,- lclosed in the application of A. Depp, vSerial No. 13,283, led March 5, 1948. A path is also completed from a :positive potential at the volt- Yage .divider comprising resistors 2 i8 and 2 l 9, `con- `ductor v22.0, No. 1 .contact of operated relay L12) and to negative battery through resistor 22| whereby a positive potential is applied to the rehtfhand ,control anode of tube'LA.(.2).

'The -right-.hand control cathode of tube-"LMD ,connected to negative battery :via conductor `22%. vand through the lockeout impedances 223 and 5224. The mai-n .cathode of tube LAQ) is connected to ground through resistor 225 and also .via .conductor 223, No, l .contact .of relay 60(2) No. 4 .contact oi relay '11(2), resistor 227, wind..- ing of relay RG! .(2) vand to Vconductor 22B which 4is 4grounded :through'the front contact of operated relay 39.4 -in the originating actuator shown in Fig. :3. Therefore, tube LAQ) will undergo .a control gap discharge between the right-hand .control anode and rightshand control cathode 2,350,888 .granted to N. I. Hall on June 6, 1944.

Relay PvC'U), in operating, locks to positive battery through its No. 2 .contact and the No. l2 ,contaetof relay-@0(2) and :this positive voltage .extinguishes tube LAW). The line rcir-'cuit*lucie-f vout ris maintained, however. since 'the voltage.

vdrop in elements 223 and 221| is maintained by the connection of the positive potential on conduct-or 220 to conductor 222 upon the closure of the No. l contact of relay RC| (2). Relay RCI (2), in operating, also applies ground through its No. 3 contact to conductor 230 to signal the originating actuator (Fig. 3), and applies ground through its No. 4 contact to operate relay RC(2) Relay RC(2) in operating, disconnects the tip and ring conductors 209 and 2|0 from ground and the winding of relay L(2), respectively, and extends these leads via conductors 23| and 232, respectively, to the originating actuator (Fig. 3). Relay L(2) thereby releases. Relay RC(2), in operating, also connects ground through its No. 7 contact to conductor 233, which is common to all line circuits, to signal the originating receiver (Fig. 3).

In a manner fully described in the above-cited application of Brewer-Bruce and the above-cited patent granted to Malthaner-Vaughan, and applications and patents therein cited, the originating actuator and originating receiver (Fig. 3) then function, the former serving to transmit li-cycle alternating current over the tip and ring conductors on a simplex basis. to subset 204. As a result, the subset generates pulse position signals in accordance with its settings and these signals are passed from the originating actuator to the originating receiver 30|. The originating receiver 30| receives the called partys designation and then transfers the oiiice code designation to the originating register (Fig. 3.)

. 4 Relay 302, in the originating receiver, is then operated. Relay 302, in operating, releases relay 2 3, which removes the line tube main anode battery supply to prevent any of the line tubes from seizing the originating receiver until the receiver has restored to normal. Relay 302, in operating, also operates the connector 305 to link the receiver to the trunk number group, assuming that circuit to be idle, and locks out other receivers.

Connector 305 then applies positive battery, assumed to be positive 10U-volt battery, to conductor 30B, No. 6 contact of operated relay RC(2) in the utilized line circuit 200, to ground through the winding of relay Y(2), and through resistor 236 to ground, in parallel, through capacitor 231' and the winding of relay X(2). Relays X(2) and Y(2) will thereby be operated, but relay X(2) is slow to operate by virtue of the shunting capacitor 23T.

Relay X(2), in operating after a delay interval applies a line mark to the associated line frame primary switches. ing, applies negative battery, assumed to be negative 10G-volt battery, through its front contact, primary (right-hand) winding of marginal relay CCR2), sleeve lead 233, and to the left-hand electrodes of gaseous diodes LPIAUI) and LPBAM) and of other diodes (not shown) of the primary switch M2 of line frame #I0 for a purpose hereinafter to be described. Since the negative battery connected to varistor 250 is of a less negative potential than the negative battery at the contact of relay X(2), no current will ow through the secondary (left-hand) Winding of relay CO (2) and therefore relay COI (2) will not be operated at this time.

It may be noted that had line circuit 20| been employed, this line mark would have been applied to electrodes in similar diodes in sections LP5(4) and LP.|(4) and other sections (not shown) of primary switch 4|3 of line frame M0, that had y.line circuit 202 been employed, this line mark Thus, relay X(2), in operatf would have been applied to sections LP|(5) and LP3 5 and other sections (not shown) of primary switch 5|2 of line frame 5|0, and in a similar manner all provided line circuits are associated with a series of sections of the primary switches in the several provided line frames. The purpose of this line mark will be discussed hereinafter.

Relay Y(2) in operating, transmits a line frame signal to identify with which frame the utilized line circuit is associated. Thus, since line circuit 200 is associated with the No. l line frame, relay Y(2), in operating, connects ground to conductor 240, winding of frame relay EID and to negative battery whereby relay Ble is operated. If a line circuit associated with line frame No. 2 had been utilized, frame relay 'H0 would have been operated, and in a similar manner, a frame relay individual to each other utilized frame is selectively operated for a purpose hereinafter to be described.

As shown in Fig. 3, a plurality of incoming and a plurality of outgoing trunks are provided. The incoming trunks are utilized in the terminating phase of a call, the outgoing trunks are utilized on the originating phase of a call. Certain of the outgoing trunks are linked to certain of the incoming trunks to provide intraoiiice loops, while others of the incoming and outgoing trunks eX- tend to other oices to provide interoce loops. The trunks are divided into trunk groups, all of the trunks in any one group having a common oflice destination, i. e., a common office code designation.

Upon the interassociation of the originating register and the trunk number group by the connector 305, the desginated trunk group is selected and tested to ascertain the busy, idle or vacant condition of that group in accordance with the disclosure of the above-cited application of Brewer-Bruce and the above-cited patent granted to Malthaner-Vaughan, and in the manner similar to that fully disclosed in the application of W. A. Cornell et al., Serial No. 114,392, led September 7, 1949.

Assuming for purposes of clarity that the oflice code of the designation of the desired called party indicates that the called subscriber is associated with this same ofiice, one of the intraolice outgoing trunks is to be selected. After the selection of the proper trunk group and the determination, as will be assumed, that at least one of the trunks in that group is idle, the trunk number group (Fig. 3) will apply a positive voltage, assumed to be approximately positive volts, via conductor 301, through all idle trunk circuits in that trunk group and those trunk circuits extend this potential to the sleeve leads of the links individual to those trunks. It is to be understood, however, that not more than one trunk in each trunk frame extends this mark. Thus, for example, the positive voltage on conductor 301 is extended through resistor 33t and to ground through capacitor 33| and the Winding of slow-to-operate relay SO(3). Upon the operation of relay SOG) the positive potential on conductor 331 is extended through certain relay contacts (not shown) and through the Winding of trunk supervision relay T.S(3) in the idle No. l. outgoing trunk 3GB to sleeve conductor 82| which is connected to the right-hand electrodes of gaseous diodes TP2A(8) TPA) and to other diodes (not shown) in primary switch 812 of trunk frame 8|0. Other trunks to which the positive voltage on conductor 307 is extended simultaneously are associated: wins othenprlmats switch Sect 'rhusfthefNoiafoutgcnsftrunlsgwhie w.v-l be assumed to be in the same trunk group asA Y No.;v L outgoing trunk, ,3 8-isfconynected Viaslag e conductor; 925; to diodes Section; CERI (:3-).f,. T1336y and' to:- other: diodeszlno. shown) in;V thel same group in'primary s iwitclisv 9 of tnunlQ- frarnef 9M;v These. voltages are appli fr .a lllllloseto be noted. immediatelylaeroi-naiter;`

It may be notedthatT had-fthe.- onigefcedeofthef desired called:` subscribens desi'giiatiom been. such: as tofindicate: a callitoaediffereI-.lt oilccg, arr-out:v goingftrunk providing aecessitofthat distantuniceY over an: nteronce. loop would hat/.ep'heernseized;v such as; the. No.v 3 outgoing brun-1o; anda-asfaras the present consideration of the originating phase?. of the; call. is` concerned, .f the:V functioning ory the cir-cuits is identicali.- 'Iihese interomce': ontgllirlgi trunks. .aref connected, to interofiicer-indeming; trunk-f in. the .other cnice.;14

Tlnis, asf.- thisf time;` a` line.` sgnalzhasfbeen, applied =vi`a conductor 2;# 0Std operateffizame relay Slik, a line= markhas been: ap'lied viagsleeye .confA ductor; Z3 to certain .o'ithe-:primary switchesot the line frame 41.0,. and .aptnurgik marle has? lucent applied.- `to.1 certain-f primany switchesaoi trunk frames;

will; besseen. hereinafter, it'fisidesrable:ztliat the; line;- framef signal be .transmitted rst: Witln the; line.: mank-andfitrunk massifs;being:transmittedA adelay. internal later.` Thusthe delaylnetworkst associated with.. for example; relay, Kfm); inf. the? utilized-line: circuit;andiwithirelayiSQG) initrunlc circuit faiiearrangetn soithatethelin'e markzand the-.trunk are; transmitted. at substantially the Sametime.

general; the switchinganettvili: comprises: linezramesgtwo; of whichlare shovnebyfwawo example-ini Eigsie and: 5;. andi trunk framestwoofzwlhich. are; showni by: Way:` on' eXaI'npl'ein` Figs: Stand 9a. Eachline-frame-andl'eacln.tnunk frame com-prises.primarwandlsecondary switches;`v Each primaryf. lin'e stvitch=and .eaclr' primaryi .tnunkf switch. has: a'..plurality of vertical? inputicolumn'sacross V:thef switch, which; -are'coniectedlfto linev andi 'trunk-r `circuits respectimalgl,r `andv plurality f oit horizontaloutput` nowsi across thei1siiitch Eanh'. ofathesa rowsf and:` columns:conipnisesithre#conf diuct'ors, two.` for' i theV lusualftalkingpath and: the

thirdl'fonfarsleevef leadi- Alt theintersetion off l eachL rowy and, column; hereinafter. calledafcrosspoint1, isiarelay: comprising anV operating. coil and vthreesets -oi"makef.cont'aots. y llwo foff: these contact sets', whenflcldsedgconne the-"*tallcingi conductos oil. an inputfcoluinnltoftletallingccnw ductors: assoeiatedwith t'lrlefparticular: output nowif Alcoldllcathode'gasfdidfis also a'ssociatedl with: .each- ,cross-'point'. relay-andi tlii'sll diode-*Lina series with-'the Winding` on :tlilifelayl is'fconn'ected betwe'eriithesleev lead: off fth vertzal iilplfciurnnlandtne sleeve lead'oftheehorifzontal outputi row; Tlielthirdlcontact set folli-the Grossi-point relay;` whenil opera-ted; fsl'iort-circ'uitsflthis associi at'edz gasdiodef f 'llhev use'off the'secross-pointgas diodes in thetsleelvefleafdslfacilitates-'thaidentie cation' and lfsel'ectionof-l -idlefpatlis 'throughfth svxritcliiitigl -networkffasldescribed hereinafter; and the short-circuitingflfoffsaidl fdiodes- Jatliopieratedf primary? switchf cross-pointsffaeilitateslthe'lholding: @f anlestallislied fconne'ctionf -lthiiougl'iftl'l 'net- Worki andi-the fm'aintenanceloiif 'ai busy-"in'dicationf` albngflsaid path duringltlie path selexsti'-viin'prcfcL esses ci? sulo'se'ql'ie'ntRcall'sar 'E'acbl secondaryi switch? islconnectedfito \frinf ame-.rises so es to provide. tellsiee @obli-Event I8? centthatltlle hesizoetal .news el@ lise-les .met terminals: and: the vertical Gewinns as Switsll outlets Eaehf .frame-.6.0m ses ainumbesofselic .m enslfseeedryswil e-Qrlee. and; .44152.

orinar be@ enact fl to." suescriberfs--ll1le eil:- cuituch.-

mi. cireultllltand two htleontel cutout rows.) which are. ,conceded-.t9- .tliei horiz zestal. .inlets el Secondary' Switches. 411.4; .and 4115-. Eiaeln .seconder-yf switch. has; tw@ terticelou tsr shown lis-wey @.fizexempl il e-interconneet conductors between p .m r-.Y .and .Secondaryswitchestneremafiet celled links. ,eaelii .link-.c0111- sistne .01.2 three Conductors are @collected that each primary- Siwith= .Olathe frame is; @2.0.1.1rI nectedf toeach secondary switchE Qn thev frame-: Infv .the specie@ einpediment ehownzby was. exampleiftlleunnelfr horizontal Quin-lit. .0fprimers switehllr is oonnectedby link .416. ,to thejlmnef. hotizontalf inlet of secondary Switch- ,fl f4; and the. lower: horizontal Qlltletoif primary switch. .4112.1 isf1C,onrlfztc. l by link lllf'lf to the. upper .horizontal :inlet of s@conditiey swinchi ne simmons .the

upnerzeutlet of; primers-Switch @lf3V isionneeted byflinlr` lletoftheflowerinletfot .secondary switch 4; A'anlflihe .lower .eutlet;.0.ff.swltvl1 .Gta3-is, coni-1 nested by'linls 418 te the lower inletolsedndern link paths; and: secondary outlets; Fori: :example:

Proceeding nomfithe trunk.; output vside.oi-:fthe;

switching networkX backwards 'thnoughz the oline; af 'similar` iiianiererrrangementis4 disclosed; .Figzff showstby-Wiay 'o fz'example; trunk: tramelf come" prising: -twof 4primary switches 85| 2? land 813i.

twd secmid'aryfswitches Mr andi'rl. 'I'henpris mar-y andsenondaryffswitches aref interconnected? nntheimannen-desor-ibcdabove fcnthesline frame; so; thaifpnlrnaryfswitnhidlisfconnectedby Blte .secendarsf-.switchdtli. andr bylink .al nto.k

secondaryv silviteli` titi-51;; :and primaryV sirvitehV dm3) connectedv bwlink. Bilifto secondary" switcln 8.1;4; .andiloyf` lvlinls'lj toisecondary; switclilil Az similarrtrunlc framefisishowninj Eig.:9:' VAllzlziougna only: twol' primary-aand :twoA secondary switches; each;hadinet-Erg.'inl/oiinle-ts and-two; outletsiare; shown orf each framitfisto befunderstoodthat botlnthe number .otswitchesr andithe; numbeni: ofc? outlets; andin'lets per switch mayberneadily. expandedi aesimirrifregtngurs ammyzof .csss-pontssexf-L 75.' inlanllobvious mannenso:asito'fproyidelswitclies and frames of any desirable size, and any desir# able number of switching frames may be provided having a number of trunk connections consistent with the operating times of the system and the amount of traffic to be handled and having a similarly consistent number of primarysecondary link paths and secondary outlets. For example, trunk frames might be provided comprising ten primary and ten secondary switches, each primary and secondary switch having ten outlets and ten inlets.

Connections are made between the secondary line frame switches and the secondary trunk frame switches to provide talking paths between each line frame and each trunk frame. Thus the talking conductors 426 and 42| from the lefthand vertical of the secondary switch 4M of line frame 41B are connected directly to the righthand vertical of the secondary switch 8|4 of trunk frame 81B; the talking conductors 524 and 425 from the right-hand vertical of the secondary switch 4|4 are connected directly to the lefthand vertical of the secondary switch S14 of trunk frame SIB; and the talking conductors extending from the other outputs of line frame secondary switch 4|4 and from the outputs of the other line frame secondary switches are also connected to the vertical columns or" the trunk frame secondary switches. The line frame secondary switches and the trunk frame secondary switches may be interconnected in any suitable manner, an exemplary arrangement being shown. It may be noted that each line frame secondary switch has connections to a secondary switch on each shown trunk frame.

In addition, the third or sleeve lead of each group of conductors extending from a vertical of each of the line frame secondary switches is connected to one of the verticals of the trunk frame secondary switches in a group with its associated talking conductors to form an interframe link. Thus, for example, sleeve lead 422-822 is grouped with talking conductors 428 and 42| and the sleeve lead 426-926 is grouped with talking conductors 424 and 425. Each of the sleeve leads is provided with a unidirectional current conducting device or varistor for a purpose hereinafter to be described. rThus, for example, varistor 60| is intermediate sleeve conductors 422 and 822 and varistor B32 is intermediate sleeve conductors 1126 and 926. These elements are symbolically represented so that the arrow points in the direction of low impedance to conventional current flow.

In the disclosures of the above-identified application of Brewer-Bruce and the above-cited patent granted to Malthaner-Vaughan, a junctor circuit was provided for each talking path. These junctors performed among other functions, the relaying of supervision from the trunk circuits. In the disclosure of the subject invention, the junction means are labeled mactors, a term coined to connote that the apparatus performs both matching and connecting functions as will be seen hereinafter. These mactors, however, no longer perform the operation of relaying supervision, that function being relegated to other circuits, and consequently it is not required that a mactor be provided for each talking path. As will be seen in detail hereinafter, each mactor may be common to two or more talking paths. In a full scale installation, each mactor may be shared by ten talking paths, for example, whereby only 'one-tenth of the number of such circuits formerly employed are now required. In

ldividual ones of the provided mactors.

20 addition, each mactor circuit is considerably simplified to provide a junction means of greatly reduced cost.

In the disclosed embodiment of the invention, each mactor is shared by two talking paths, one extended from each depicted line frame, although it is to be understood that this is but exemplary as above noted. Mactor No. 1 (Fig. 6), shown in detail, is selectively associable either with the talking path comprising tip and ring conductors 420 and 42| which extend from the left-hand vertical of the line frame secondary switch 4|4 or with the talking path comprising tip and ring conductors 520 and 52| .which extend from the left-hand vertical of the line frame secondary switch 5|4.

This selective association is accomplished by means of the aforesaid frame relays EN) and lll), and others (not shown). As before mentioned, if the subscribers line circuit is in line frame No. l, a. signal is transmitted to operate relay Bi whereas if the employed line circuit is in line frame No. 2, a signal is transmitted to operate relay IIB. If relay Sid is operated, the sleeve lead 822 is connected through the No. 1 contact of that relay to conductor 623 which extends to mactor No. 1; sleeve lead 926 is connected through the No. 2 contact of relay 6|@ to conductor 6l4 which extends to mactor No. 2; and so on, with the sleeve conductors of each interframe link extending from line frame No. l being connected to in- Similarly, if relay im had been operated as a result of the utilization of a line circuit in line frame No. 2, sleeve lead 922 would have been connected through the No. 1 contact of that relay and via conductor 603 to mactor No. 1, sleeve lead 826 would have been connected through the No. 2

`contact of relay '|I0, and via conductor 604 to mactor No. 2, and so on, with the sleeve conductor of each interframe link extending from line frame No. 2 being connected to individual ones of the provided mactors. A frame relay, such as relays Bl and H0, is provided for each line frame and is operative to associate the interframe links from that frame with the provided mactors. Thus, only one set of mactors is required even though several irames be provided.

As will be seen in detail hereinafter, a fourth or control lead is extended from each of the vertical columns of the secondary switches of the line frames. The control conductors in corresponding elements of the several line frames are multipled to extend to individual mactors. Thus, control lead 423 extends from the left-hand vertical of secondary switch M4 in line frame No. 1 and from the left-hand vertical of secondary switch 5 I4 in line frame No. 2 and is connected to mactor No. 1. Similarly, control lead 421 extends from the right-hand vertical of secondary switch 4I4 to mactor No. 2 and also from the right-hand vertical of secondary switch 5|4 to mactor No. 2. These control conductors are also common to the corresponding elements of all other provided line frame secondary switches. In a similar fashion, control conductors from other line frame secondary switch elements extend to the other provided mactors.

As hereinbefore described, under the assumed conditions a negative Voltage line mark is applied to sleeve lead 238 which is connected to the left vertical of line switch 4|2 and a positive trunk mark is applied to sleeve leads 82| and 920 which are connected to the verticals of trunk primary switches SI2 and SI2, respectively. As-V 

